1. Field of the Invention
The present invention relates to probe cards for testing semiconductor chips and, more particularly, to an automated system and method for locating the tips of probes on a probe card so that if any of the probe tips are out of proper alignment, they can be adjusted back into proper alignment.
2. Discussion of Prior Art
In FIG. 1, a conventional probe card 10 is shown being rectangular in shape A variety of conventional shapes exist for a probe card. Probe card 10 illustrates a certain number of probes and any number of probes may be provided such as 100 through 500 probes per card. The shape of a probe card, the number of probes utilized, and the geometric placement of the probes is entirely dependent upon the topological structure of the semiconductor chip for which the probe card is designed. The probe card 10 of FIG. 1 is merely set forth as one conventional example.
Probe card 10 is essentially a printed circuit card having a number of pin connections 20 interconnected over printed circuit paths 30 to a desired geometric configuration of probes 40 located around a defined region 50. This defined region 50 having the probes 60 downwardly extending therein is better shown in FIG. 2.
In FIG. 2, each probe 60 has a tip 70, an angled body portion 80, and a horizontal portion 90. The horizontal portion 90 is soldered 100 to a pass through conductive path 110 connected to the printed circuit path 30. Other conventional probe cards are soldered on the top of the card. A support ring 120 is utilized to firmly engage the horizontal portion 90 of each probe around the defined region 50. Each probe 60 is carefully oriented to downwardly extend into the defined region 50 so that each tip 70 is placed in the same plane 130 at an assigned position or point 140 in plane 130. Hence, when the probes 60, as contained in the card 10, are lowered onto a semiconductor chip which would occupy plane 130, the probe tips 70 engage pads on the chip at precise and desired locations. Of course, the location of the plane 130 can exist within a desired range 140 and each tip 70 can exist within a given range 160 of its assigned position 140 on the plane.
After significant use of the probe card 10 in testing semiconductor chips, and as discussed above, a probe tip 70 may move out of its assigned position 140 and plane 130. This is graphically illustrated in FIGS. 3 and 4 wherein the pin 60a has been bent downwardly to occupy a new plane 130' and a new position in the plane 140a'.
Under the teachings of the prior art approach, and as shown in FIG. 3, an operator would view the tip 70a through a microscope 330 as it engages the pad 300 of a silicon chip 310. The operator would view the location of each probe tip to the underlying pad on the silicon chip and this process could take considerable time. In addition, the operator would subjectively imagine a centering window 160 on the pad 300 and if the probe tip 70a fell outside the window 160, then the operator would use a tweezers to manually move the tip 70a of probe 60a in the direction of arrow 400 as shown in FIG. 4. It would be the goal of the operator to continue this process until the probe tip 70a occupies a desired position 140 within the window 160 of the pad 300. It is to be understood that the probe tip may be in any unaligned position such as for example above plane 130.
The article "Automating Probe Card Analysis and Maintenance" by Ralph W. Smith and Jesse Hendrickson, discusses the use of probe cards to test semiconductor chips and systems to maintain and repair such probe cards. Commercially, systems are available for the automatic analysis, maintenance and repair of probe cards such as the PACER from Triple S Engineering, Inc., 1042 Elkton Drive, Colorado Springs, Colo. 80907, the COMPASS from Wentworth Laboratories, Inc., 500 Federal Road, Brookfield, CT 06804, and the PROBILT 500 from Probe Technology, 3000 Olcott Street, Santa Clara, Calif. 95054.
3. Statement of the Problem
A need exists for a fully automatic system for accurately locating the tips of probes on a probe card and to minimize or eliminate operator subjectivity in determining probe alignment.
A search of prior patents directed to the above-identified need was conducted which resulted in the following patents:
______________________________________ Russell 4,342,958 August 3, 1982 Russell 4,342,957 August 3, 1982 Stewart, et al 4,918,374 April 17, 1990 ______________________________________
Of the patents uncovered, only U.S. Pat. No. 4,918,374 is pertinent to the teachings of the present invention. This patent sets forth a method and apparatus for inspecting integrated circuit probe cards. In the '374 patent, the tips of probes in probe card are scanned across a check plate having a conductivity transition border. This results in the generation of two conductivity values in the X direction and two conductivity values in the Y direction. A pair of conductivity values are generated in each direction when a probe tip first "makes" contact with the conductivity transition border and when it "breaks" conductivity with the conductivity transition border. All probe tips are scanned across the conductivity transition borders at the same time. The '374 provides an approximation as to the actual probe tip location.
A need exists to individually sense the precise position of each probe tip and to display, via a computer monitor, the actual location of each individual probe tip. Hence, a need exists for a fully automatic system for individually and precisely locating the tips of each probe on a probe card and for displaying the results visually for an operator to manually adjust the probe tip into alignment.
4. Solution to the Problem
The present invention provides a solution to the above problem by providing a system and method for individually measuring the actual X, Y position of each probe tip in a probe card and comparing it to an assigned X, Y position thereby eliminating operator subjectivity in making such determinations. The system and method automatically measures each probe tip and displays the results in a computer monitor for an operator to quickly view which probe tips are out of alignment. The operator can cause the system and method of the present invention to display the precise location, as measured by the present invention, of a tip with respect to its assigned X, Y position so that the operator can know in which direction and how much the probe tip should be adjusted. The system then checks to verify that a proper alignment by the operator has been made. If not, the operator is instructed to realign the probe tip.